Spectroscopic analysis generally relies on detection and quantification of emission or absorption of radiation by matter. The radiation is absorbed or emitted with a particular energy determined by transitions occurring to the molecules of an analyte. For example, in infrared spectroscopy, discrete energy quanta are absorbed by molecules due to excitation of vibrational or rotational transitions of the intra-molecular bonds. The collision of other molecules in a gas mixture with the emitting or absorbing molecules and the collision between the emitting or absorbing molecules themselves can perturb the energy levels of the emitting or absorbing molecules and therefore cause broadening of the emission or absorption line shape. Collisional broadening of spectral line shapes can depend on any or all of the pressure, temperature, and composition of the gas mixture in addition to the spectral transition and concentration of a particular target analyte. Furthermore, absorption of the discrete energy quanta by components of a sample gas other than the target analyte can also structurally interfere with the measured emission or absorption line shape. Quantitative measurement errors can occur if the spectroscopic analyzer is used to measure a target analyte in a sample gas having one or more of a pressure, a temperature, and a background composition (e.g. concentrations of other compounds in the sample gas than the target analyte) that differ from the gas mixture used to calibrate the analyzer. These errors have been found to be a substantial challenge for optical measurement of trace level impurities (e.g. less than approximately 10,000 ppm) in natural gas quality control, petrochemical production, quality control and environmental emissions control, and the like, but is not limited to those applications.